请问Android在UI线程中启动新线程复制文件，为何还会使界面延迟 ？

new Thread(new Runnable() {
 @Override
 public void run() {
 // TODO Auto-generated method stub
 // 把sql文件写入sd卡，然后把路径给so
 String mPath="";
 if(android.os.Environment.getExternalStorageState().equals("mounted")){
 mPath = android.os.Environment.getExternalStorageDirectory().toString()
 + "/com.newhaoli.Teamtips/";
 }else{
 mPath=android.os.Environment.getDataDirectory().getAbsolutePath()+
 "/com.newhaoli.Teamtips/";
 }
 // TODO Auto-generated method stub
 // 扫描或者复制整个文件夹到sd卡上
 copyDir("Query", mPath+"Workflow/");
 copyDir("htmlinc", mPath+"Workflow/");
 copyDir("Html", mPath+"Workflow/");
 }
 }).start();